1,368 research outputs found
Stellar Activity and Coronal Heating: an overview of recent results
Observations of the coronae of the Sun and of solar-like stars provide
complementary information to advance our understanding of stellar magnetic
activity, and of the processes leading to the heating of their outer
atmospheres. While solar observations allow us to study the corona at high
spatial and temporal resolution, the study of stellar coronae allows us to
probe stellar activity over a wide range of ages and stellar parameters.
Stellar studies therefore provide us with additional tools for understanding
coronal heating processes, as well as the long-term evolution of solar X-ray
activity. We discuss how recent studies of stellar magnetic fields and coronae
contribute to our understanding of the phenomenon of activity and coronal
heating in late-type stars.Comment: Accepted for publication on Philosophical Transactions A. 29 pages, 5
figure
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Apollo telescope mount: A partial listing of scientific publications, supplement 2
Reports are compilations of bibliographies from the principal investigator groups of the Apollo Telescope Mount (Skylab solar observatory facility) that gathered data from May 28, 1973, to February 8, 1974. The analysis of these data is presently under way and is expected to continue for several years. The publications listed in this report are divided into the following categories: (1) Journal Publications, (2) Journal Publications Submitted, (3) Other Publications, (4) Presentations--National and International Meetings, and (5) Other Presentations. An author index is included together with errata for the first report
Short term Variability of the Sun Earth System: An Overview of Progress Made during the CAWSES II Period
This paper presents an overview of results obtained during the CAWSES II
period on the short term variability of the Sun and how it affects the near
Earth space environment. CAWSES II was planned to examine the behavior of the
solar terrestrial system as the solar activity climbed to its maximum phase in
solar cycle 24. After a deep minimum following cycle 23, the Sun climbed to a
very weak maximum in terms of the sunspot number in cycle 24 (MiniMax24), so
many of the results presented here refer to this weak activity in comparison
with cycle 23. The short term variability that has immediate consequence to
Earth and geospace manifests as solar eruptions from closed field regions and
high speed streams from coronal holes. Both electromagnetic (flares) and mass
emissions (coronal mass ejections, CMEs) are involved in solar eruptions, while
coronal holes result in high speed streams that collide with slow wind forming
the so called corotating interaction regions (CIRs). Fast CMEs affect Earth via
leading shocks accelerating energetic particles and creating large geomagnetic
storms. CIRs and their trailing high speed streams (HSSs), on the other hand,
are responsible for recurrent small geomagnetic storms and extended (days) of
auroral zone activity, respectively. The latter lead to the acceleration of
relativistic magnetospheric killer electrons. One of the major consequences of
the weak solar activity is the altered physical state of the heliosphere that
has serious implications for the shock-driving and storm causing properties of
CMEs. Finally, a discussion is presented on extreme space weather events
prompted by the 2012 July 23 super storm event that occurred on the backside of
the Sun. Many of these studies were enabled by the simultaneous availability of
remote-sensing and in situ observations from multiple vantage points with
respect to the Sun Earth line.Comment: 85 pages, 30 figures, 2 tables, Accepted for publication in Progress
in Earth and Planetary Science on April 13, 201
Polar plumes' orientation and the Sun's global magnetic field
We characterize the orientation of polar plumes as a tracer of the
large-scale coronal magnetic field configuration. We monitor in particular the
north and south magnetic pole locations and the magnetic opening during
2007-2008 and provide some understanding of the variations in these quantities.
The polar plume orientation is determined by applying the Hough-wavelet
transform to a series of EUV images and extracting the key Hough space
parameters of the resulting maps. The same procedure is applied to the polar
cap field inclination derived from extrapolating magnetograms generated by a
surface flux transport model. We observe that the position where the magnetic
field is radial (the Sun's magnetic poles) reflects the global organization of
magnetic field on the solar surface, and we suggest that this opens the
possibility of both detecting flux emergence anywhere on the solar surface
(including the far side) and better constraining the reorganization of the
corona after flux emergence
- …